Process for the production of acetarylamides



Patented May 1, 1951 PROCESS FOR THE PRODUCTION OF ACETAKYLAMIDES- Edgar Stagg Pemberton, Banstead, England, as-

signor to British Industrial Solvents Limited, London, England, a British company No Drawing. Application January 14, 1949, se

rial No. 71,030. 20, 1945 Claims.

Thi invention is for an improvement in or:

relating to the production of acetarylamides, and is a continuation-in-part of my copending application Serial No. 696,041 filed on September 10, 1946, now Patent No. 2,462,221

Numerous methods have, in the past, been employed for the preparation of acetanilide but the method which has heretofore been used on the large scale generally consists in heating a vmixture of aniline and acetic acid (the latter being in considerable excess, for instance 50-60% excess over the stoichiometric amount) and slowly distilling off dilute acetic acid. The water in the distillate derives from the dehydration of the aniline acetate to acetanilide, and the concentrations of the acetic acid in the initial and' v the use of acetic anhydride which i an expensive substance, that the distillation of dilute acetic acid formed during reaction and the subsequent additions of fresh acetic anhydride with avoidance of overheating due to the exothermic reaction leads to as many interruptions of the manufacturing procedure.

According to the present invention there is provided a process for the production of acetarylamides comprising heating an aryl amine with an excess of acetic acid not exceeding 25% by weight of the amount theoretically required, in

the presence of a lower aliphatic acetate in an amount not exceeding about 5% by weight of the reaction mixture, effecting the reaction at temperatures between 130 and about 200 C. whilst distilling off from the reaction mixture the water of reaction in the form of-a binary mixture with said aliphatic acetate condensing the distillate, separating the said aliphatic acetate therefrom, returning the separated aliphatic acetate to the reaction mixture and finally distilling off the aliphatic acetate by distillation under substantially atmospheric pressure and disency to decomposition of the product is In Great Britain September 2 tilling off an excess of unreacted acetic acid under sub-atmospheric pressure.

As lower aliphatic acetates acetic acid esters of aliphatic alcohols with two to five carbon atoms in the molecule may be used. Such acetates are e. g. ethyl acetate, normal propyl acetate, isopropyl acetate sec-butyl acetate and iso butyl acetate.

By the process of this invention it is possible to carry out the acetylation of aniline more rapidly and with a much smaller quantity of acetic acid than has hitherto been employed. A further advantage is that at least by weight of the excess acid can be recovered in the form of anhydrous acetic acid for re-use. This means that about by weight of the acetic acid charged into the reactor i recovered either in the form of acetanilideor as anhydrous acetic acid. r

The quantity of lower aliphatic acetate that is required to carry out the process of my invention and which I shall call for convenience the entrainer is dependent on the capacity of the fractionating column, but is relatively small and may, for example, be as low as 23% by weight of the total reaction mixture.-

The production of acetanilide, for example, may be carried out by charging into, the reaction vessel (preferably fitted with an efficient fractionating column) a mixture of the whole of the aniline, entrainer and acetic acid required for the process and heating the mixture until evaporation ofthe entrainer-water binary mixture begins. I prefer to add the whole of the acetic acid at the commencement of the operation rather than to add the acid gradually throughout the reactions as the latter process involves a considerable lengthening of the time required to bring the reaction to completion.

As the reaction proceeds the entrainer-water vapourdistilling off through the fractionating column is condensed and is allowed to separate into two layers, the upper layer of entrainer being returned to the reaction vessel or column.

' When no more water distils off the residual en-- trainer is finally distilled off and excess acetic acid recovered from the reaction vessel by distillation under subatmospheric pressure. Any tendthereby avoided.

Catalysts may be employed in the reaction if desired, but I have found that the reaction pro ceeds satisfactorily in their absence. The reaction may be carried out at a temperature between and about 200 0. preferably 0.1% by weight (reckoned as acetic acid).

starting near the lower temperature of this range. As the reaction proceeds towards completion it might be necessary to raise the temperature within these limits.

After removal of the water is completed the excess of entrainer is recovered by distillation at substantially atmospheric pressure. way the loss of the entrainer is cut down toa minimum. As previously stated the acetic acid recovery is conducted under reduced pressure, for instance at a pressure of 110430 mm. of mercury. At this pressure the boiling point of the acetanilide is about 30 C. above that employed for stripping ofi the entrainer at atmospheric pressure so that a heating system suitable for acetylation and entrainer stripping would suflice for the stripping of the acetic acid. Thus a grade of acetanilide suitable for sale can be made in one vessel with a minimum amount of handling.

The product obtained in the above manner is suitable 'for most industrial purposes. The molten anilide may be run off on to a flaking device. It is characterized by an acidity below y the process of my invention it is easily possible to obtain a product which is completely neutral in reaction. Any further purification required may be eflected, for example, by vacuum distillation.

The following examples illustrate the manner in which the invention may be carried into effect:

Example 1 Into a flask fitted with a 13-section Young and Thomas Evaporation Column were charged 7 moles of aniline together with acetic acid (21% by weight in excess of that theoretically required) and isopropyl acetate equal to 6% of the weight of the total anilineeacetic acid mixture. The liquid reaction temperature was varied between 160 and 172 C. during the distillation of the isopropyl acetate-water mixture whilst the acetic acid recovery took place up to a ,liquid temperature of about 240 C. under 110430 mm. pressure. The reaction was complete in 21 hours and a product having an acidity of 0.1% (as acetic acid) was obtained in 99.5% Yield based on the aniline. The anilide has a melting point of 113.5 C. In this example all the acetic acid was fed into the refluxing isopropyl acetateeaniline mixture.

Example 2 In a-further experiment conducted with 21% by weight excess of the theoretically required amount of acetic acid and only 4% byweight of isopropyl acetate (reckoned as in Example 1), the reaction was conducted at a temperature of 133 to 190 C., whilst the stripping of the acetic acid took place up to a liquid temperature of about 232 C. at 100 mm. pressure. The product which was obtained in 99.7% yield based on the aniline, was neutral in reaction and melted at 113.5 C. In this experiment 70% by weight of the acetic acid was fed in initially, the remainder being fed in as the reaction proceeded. The reaction was completed in about 8 hours.

Eqrample 3 In a furtherexperiment all the reactants coneining 22.4% by weight excessof thetheoreti- In this cally required amount of acetic acid and 4% by weight of isopropyl acetate (reckoned as in Example 1) were mixed initially, the reaction being conducted at a temperature of 135 C. whilst the stripping of the acetic acid took place at mm. mercury pressure. The product obtained in 99% yield based on the aniline was neutral and .melted at.114. C. 8 hours sufliced for the completion of the reaction.

Example 4 428 parts by weight of ortho-toluidine were mixed with 288 parts by weight of glacial acetic acid (beingan excess of 20% over the theoreti cal amount) and 40 parts by weight of isopropyl acetate (5.6% by weight reckoned as in Example 1) and kept for 9.5 hours at a temperature of about 140 C., gradually raising it to 232 C. whilst the isopropyl acetate-water mixture is distilled off and acetic acid recovered as described in the preceding example. The yield of ortho-acet-toluidide based on orthc-toluidine is 99.4%; on the acetic acid about 95%. The melting point of the product obtained is between 103 and l06.5 C.

Example 5 428 parts by weight. of meta-toluidine were mixed with 243 parts by weight of acetic acid (an excess of 18% of the amount theoretically required) and 44 parts by weight of isopropyl acetate (about 5% by weight reckoned as in EX- ample 1), the temperature range was from 132-215 .C. The reaction was completed in 7.5 hours. The yield based on toluidine was 99.4%, based on acetic acid it was 96.4%, The product .melted at 63-64 C.

I. claim:

1. A process for the production of acetarylamides which comprises heating an arylamine with an excess of acetic acid not exceeding 25% by weight of the amount theoretically required in the presence of an amount of a lower alkyl acetate not exceeding about 5% by weight of the reaction mixture, effecting the reaction at temperatures between C. and about 200 .6. Whilst distilling off from the reaction mixture the water of reaction in the form of a binary mixture with said lower alkyl acetate, condensing the distillate, separating the lower alkyl acetate therefrom, returning the separated lower alkyl acetate to the reaction mixture and finally distilling oil the lower alkyl acetate by distillation under substantially atmospheric pressure anddistilling ofi excess of unreacted acetic acid under sub-atmospheric pressure.

2. Aprocess according to claim 1 wherein the lower alkyl acetate isisopropylacetate.

3. A process accordin to claim 1 in which the arylamine is aniline.

4. A process in accordance with claim 1 in which the arylamine. is ortho-toluidine.

5. A process in accordance with claim 1 in which the arylamine is meta-toluidine.

EDGAR STAGG PEMBERTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,462,221 Pemberton Feb. 22, 1949. 

1. A PROCESS FOR THE PRODUCTION OF ACETARYLAMIDES WHICH COMPRISES HEATING AN ARYLAMINE WITH AN EXCESS OF ACETIC ACID NOT EXCEEDING 25% BY WEIGHT OF THE AMOUNT THEORETICALLY REQUIRED IN THE PRESENCE OF AN AMOUNT OF A LOWER ALKYL ACETATE NOT EXCEEDING ABOUT 5% BY WEIGHT OF THE REACTION MIXTURE, EFFECTING THE REACTION AT TEMPERATURES BETWEEN 130* C. AND ABOUT 200* C. WHILST DISTILLING OFF FROM THE REACTION MIXTURE THE WATER OF REACTION IN THE FORM OF A BINARY MIXTURE WITH SAID LOWER ALKYL ACETATE, CONDENSING THE DISTILLATE, SEPARATING THE LOWER ALKYL ACETATE THEREFROM, RETURNING THE SEPARATED LOWER ALKYL ACETATE TO THE REACTION MIXTURE AND FINALLY DISTILLING OFF THE LOWER ALKYL ACETATE BY DISTILLATION UNDER SUBSTANTIALLY ATMOSPHERIC PRESSURE AND DISTILLING OFF EXCESS OF UNREACTED ACETIC ACID UNDER SUB-ATMOSPHERIC PRESSURE. 